Displaying polylines in different color / Color gradient

Though i am using QGIS, yet I am not confined by tool (can use an entirely different tool or a plugin for QGIS) usage.. Only aim is to get the following:

I am reading various shapefiles in QGIS and I wish to have different colors in the same shapefile (or layer) for -

1. Each polyline


2. Every n number of polylines


3. A chunk of n points in a single large polyline.

Any help appreciated.